From the ABC 7 Weather team

Next storm to affect areas northwest of D.C. Tuesday night

February 3, 2014 - 02:57 PM
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First the area received a mix of rain and snow across the region. This time around, icing seems to be the main concern, especially northwest of D.C.

As one weak storm departs the region with light snowfall in its wake for parts of the area, it's time to focus on the next system, which will enter the region tomorrow night. This new system again looks to have wintry precipitation involved, but it appears like it will hit the same places that saw today's snow and leave D.C. with less of a threat.

Winter Storm Watch for parts of the D.C. area

A Winter Storm Watch is in effect for areas northwest of D.C. once again, with the biggest threat being up to a quarter of an inch or more of ice.

The next system will be different from today's, as low pressure will ride northeast along the spine of the Appalachians west of D.C. and a new area of low pressure will eventually form and take over off the east coast. *Nerd Alert* - You can impress your friends and tell them this will be a case of Miller Type B cyclogenesis.

Forecast 12Z GFS MSLP, 6hr precip and 850mb temps (Courtesy: NEXLAB Models)

High pressure will shift to the north of D.C. tomorrow helping supply cool, dry air at the surface through the day. Winds will shift to out of the northeast and a cold pool will begin to set up east of the mountains. Precipitation often acts to strengthen the cold pool as Cold Air Damming (CAD) takes over. You can see the CAD in the kinks in the isobars just east of the Appalachians in this model forecast for late Tuesday.

Warmer air will be located above the surface, with 850mb temperatures a few degrees above freezing, but at the surface, temperatures should be at or below freezing for much of the region at the onset of precipitation. This will lead to rain falling on frozen surfaces and freezing on contact.

4km NAM Forecast reflectivity for Wednesday morning around 1am (Courtesy: WeatherBell Models)

For the D.C. Metro and points southeast, temperatures should jump above freezing by sunrise, but a few slick spots may still be possible for the commute Wednesday morning. Areas northwest will have the opportunity for freezing rain to hang on in the region even longer, and significant icing may be possible along and west of the Blue Ridge Mountains particularly in the shallow valleys where cold air gets trapped at the surface.

We'll keep a close eye on this over the next 12 hours and have the latest updates on ABC 7 News at 5, 6 and 11pm.

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